The present invention relates to an organic nanotube which has a hollow fibrous form with an inner pore diameter of 10 to 20 nm, an outer diameter of 40 to 80 nm and a length of several tens xcexcm to several hundreds xcexcm, and which finds usefulness in the industries of fine chemicals, medicines and cosmetic and toiletry preparations as well as in the electronic information technology, energy industry and chemical industry, and also relates to a method for the preparation thereof.
A lipid of certain types self-assembles to form a stable molecular aggregate and is utilized as a functional material in fine chemical and medical fields. Such a lipid or, for example, the so-called ribosome which is a spherical aggregate comprising a phospholipid derived from a natural origin is produced by the thin film method, thermal dispersion method, solution injection method, cholic acid method or reverse layer method. These methods are all complicated and must use technologies requiring skillfulness. This offers difficulties in putting these methods into practice. Also, because molecular aggregates obtained by these methods all have a spherical morphology so that a hollow fibrous molecular aggregate having a large axial ratio, which is the ratio of the width to length of a fiber, cannot be obtained and consequently the application fields where these molecular aggregates are used are inevitably limited.
On the other hand, it is known that a fibrous or rod-shaped molecular aggregate is obtained by dispersing a synthetic amphiphilic compound in water [xe2x80x9cJournal of American Chemical Societyxe2x80x9d, Vol. 107, pages 509-510 (1985)].
However, although the molecular aggregate obtained by this method has a ribbon- or string-like fiber form, it is impossible to produce a nanotube structure having a uni-dimensional isolated void and a large surface area to be effective for gas storage and isolation of useful biomolecules and therefore has almost no utilizability as a fibrous molecular aggregate.
The present invention has been made with an object to provide a novel hollow fibrous organic nanotube which can be produced by a simple method from an inexpensive and renewable resource-based natural material of good availability along with regenerability and has a wide range of applicability.
The inventors of the present invention have repeatedly conducted extensive studies concerning a method of forming a functional material having a wide range of applicability simply from an easily available material and, as a result, found that an organic nanotube having a hollow fibrous structure can be obtained by causing molecular aggregation of an O-glycoside type glycolipid, in which the aglycon is a long-chain alkylphenol isolated from cashew nut shell liquid or a derivative thereof, by using several different methods and followed by quasi-crystallization of the glycolipid. Based on this finding, the present invention has been completed.
Accordingly, the present invention provides a hollow fibrous organic nanotube having an inner pore diameter of 10 to 20 nm and an outer diameter of 40 to 80 nm, the nanotube comprising an O-glycoside type glycolipid having an aldose residue as the glycosyl group and a group represented by the general formula: 
wherein R represents an unsaturated straight-chain hydrocarbon group having 12 to 18 carbon atoms, as the aglycon. The present invention also provides a process for producing the hollow fibrous organic nanotube having an inner pore diameter of 10 to 20 nm and an outer diameter of 40 to 80 nm, the process comprising the steps of dissolving the above O-glycoside type glycolipid in water at an elevated temperature to saturation, cooling the aqueous solution gradually and allowing the solution to stand at room temperature to cause spontaneous molecular aggregation and quasi-crystallization.